1. Field
Example embodiments of inventive concepts relate to memory systems, and more particularly, to memory systems having failed memory cells and methods of managing failed memory cells.
2. Description of Conventional Art
A dynamic random access memory DRAM or a magnetic random access memory MRAM can be used as a main memory of a memory system.
In a DRAM, a failed memory cell may exist in a memory cell array. A hard-failed memory cell among failed memory cells is replaced with a spare memory cell through a repair process.
A soft-failed memory cell among failed memory cells can be divided into a faulty memory cell and a weak memory cell. In the case that a faulty memory cell exists in a memory cell array, a masking off operation of inhibiting an access operation with respect to a corresponding memory cell is desired. In the case that a weak memory cell exists in a memory cell array, since its operation is similar to an operation of a normal memory cell having relatively high reliability of data access, a relatively frequent refresh operation may be desired.
However, a frequent refresh operation of a weak memory cell may increase power consumption.
A unit of memory that is masked off when a faulty memory cell or a weak memory cell occurs may be a page frame unit, which includes a plurality of memory blocks of a memory cell array. However, masking off a plurality of memory blocks due to one failed memory cell results in wasted memory capacity.